do not use the NPX registers to optimize copyin or copyout.
The NPX registers are normally used to optimize copying and zeroing when all of the following conditions are satisfied:
.Cd "cpu I586_CPU" is an option
the CPU is an i586 (perhaps not a Pentium)
the probe for npx0 succeeds
INT 16 exception handling works.
Then copying and zeroing using the NPX registers is normally 30-100% faster.
The flags can be used to control cases where it does not work or is slower. Setting them at boot time using userconfig works correctly (the optimizations are not used until later in the bootstrap when npx0 is attached).